High quality molecular beam epitaxy growth and characterization of lead titanate zirconate based complex-oxides

Author

Xing Gu, Virginia Commonwealth University

DOI

https://doi.org/10.25772/S74Q-T130

Defense Date

2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Electrical Engineering

First Advisor

Hadis Morkoç

Abstract

Research interest in complex oxides has resurged owing to progress in modern epitaxial techniques. Among such oxides, lead-titanate-based thin films such as PbTiO₃ (PTO) and Pb(Zr_xTi_1−x)O₃ (PZT) offer attractive advantages for a wide variety of applications. Moreover, integration between functional oxides with compound semiconductors has the potential to realize multi-functional devices which enjoy the properties from both groups of materials. Ferroelectric materials with a perovskite structure (ABO₃) and semiconductors such as GaN with a hexagonal structure, require a careful choice of a bridge layer and suitable epitaxial technique. Molecular beam epitaxy (MBE) has been an established technique in providing epitaxial growth with high crystal perfection and precise control over material composition. Single-crystal oxides grown by molecular beam epitaxy (MBE) can in principle avoid grain boundaries and provide a sharp interface as well.

In this dissertation, the MBE growth mechanism of PZT was investigated. In-situ RHEED patterns indicate that the growth of PTO and PZT occur in a two-dimensional, layer by layer mode, as confirmed by a streaky pattern. The crystal quality of PTO, PZO, and PZT thin films prepared by MBE are evaluated by X-ray diffraction (XRD), and have a full width at half maximum (FWHM) value of 4 arcmin for an 80nm thick layer. Optical properties of the PTO thin films have been characterized by variable angle spectroscopic ellipsometry (VASE), and well resolved dielectric functions are extracted. The refractive index is determined as 2.605 at 633 nm, and bandgap energy as 3.778eV. The electrical properties of the PTO and PZT are evaluated by the measurement of polarization-field hysteresis loops, give a remanent polarization of 83 μC/cm² and a coercive field of 77 kV/cm. Lead oxide (PbO), titanium dioxide (TiO₂), and zirconium dioxide (ZrO₂), on GaN templates for potential PZT/GaN integration. The epitaxial growth of TiO₂, PbO, and ZrO₂ is realized on GaN templates for the first time by MBE. The PbO epitaxial layer was also used as a nucleation layer to enable single crystalline, perovskite PTO growth on GaN.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

August 2008